The present invention relates broadly to achieving higher recording track densities on data recording members, or recording media, and to track-following and track-identifying techniques. More particularly, it relates to improved servo-positioning recording formats and methods of recording such servo-positioning formats on recording members. Still more particularly, in the most preferred form, the invention relates to improvements in techniques for initializing the storage medium prior to its intended use by prerecording track-identifying and track-centering servo information thereon, and to the improved record format itself as well as the method of embedding the servo-recording format along the recording track, particularly in conjunction with magnetic tape but in a broader sense with other forms and types of record members, or media, such as disks.
In the use and continued development of moving-media data-memory devices, particularly magnetic tape and disk drives, substantial effort and progress continues toward the goal of increasing the amount of data stored on a given surface area of the recording member. Embedded servo techniques have been developed as a result of these efforts which utilize closely-spaced positioning information, recorded on the storage medium prior to its use for actual data storage operations, to individually identify each of a plurality of closely-spaced tracks on the storage medium. A closed-loop servo-positioning system may be used to follow the prerecorded tracks, thereby increasing the number of data tracks per given area by allowing a narrowing of the data tracks themselves and permitting the placement of data tracks closer together. Known and related servo-positioning systems having a number of significant advantages are disclosed in U.S. Pat. No. 4,472,750, entitled DATA RECORD WITH PRE-RECORDED TRANSDUCER POSITIONING SIGNALS AND TRANSDUCER USING THE SAME, issued to Klumpp et al. on Sep. 18, 1984; and U.S. Pat. No. 4,586,094 entitled, METHOD AND APPARATUS FOR PRE-RECORDING TRACKING INFORMATION ON MAGNETIC MEDIA, issued to Chambors et al. on Apr. 29, 1986, the disclosures of which are incorporated herein by reference.
Although significant increases have been made in the number of tracks which can be provided on magnetic tape storage media, lateral tape motion during lengthwise operating transport remains a significant impediment even where prerecorded servo-tracking signals are used together with closed-loop servo systems. Lateral excursions of a rapid nature or comparatively large magnitude, may occur during stopping and starting conditions, in addition to the excursions which occur during steady-state longitudinal transport of the tape, and all of these make accurate tracking by the transducer particularly difficult. In addition to these lateral excursions, longitudinal tape speed variations and the like also occur, since recording tape is typically under tension as it is transported lengthwise and the tape is subject to varying amounts of stretching during transport, making accurate longitudinal positioning of signals on the tape difficult. For example, wide variations in the tension on magnetic-tape media occur when transport of the tape is stopped and started. Because of the somewhat random occurrence and presence of such conditions, accurate positioning of the transducers relative to the tape itself for recording ("writing") the servo-tracking signals used by the servo system becomes increasingly difficult, and an increasingly important factor, as the track density increases.
Track-centering servo information in accordance with the above-mentioned incorporated prior patents and other such state-of-the-art systems was primarily recorded on the magnetic medium using a single-gap transducer, by which the track-identification signals and track-centering signals were recorded in sequential form on the recording member, one track at a time. Consequently, formatting an entire tape requires repeated passes over its length, which significantly increases the time required to complete the formatting and requires a very large dumber of times that the transducer is switched on and off to write the numerous different bursts. The repeated stopping and starting of the storage medium at the ends of each such run causes relatively wide variations in both the lateral and longitudinal position of the medium during transport, as described above, and thus increases the difficulty of accurately positioning the transducer to record the different signal bursts precisely at the desired locations, to define straight and closely-adjacent tracks with accurately-spaced servo signals therealong. Additionally, even the most accurate recording system has difficulty positioning the transducer such that centering signals in adjacent tracks are aligned with each other across the recording member. This difficulty, amounting to a practical inability to laterally and longitudinally align the centering signals, resulting in a potential for lateral and longitudinal overlap of servo-centering signals which must be spaced from one another to identify track centers, has also helped prevent further reductions in the widths of the tracks as well as the distance between the tracks.
An additional limitation of servo systems utilized heretofore, is that the track-identification signals were usually recorded in groupings with track-centering signals, whereby the tracks may be identified as part of the procedure of transducer centering and track following by the servo system. By providing the track-identification signals along with the servo-tracking signals, the tracks may be identified each time the transducer position is monitored. However, the recording of track-identification signals on the recording medium each time servo-centering signals are recorded significantly increases the amount of recording surface area which is dedicated to the servo-positioning signals, and consequently reduces the surface area which may be used for data storage.